The next generation of wireless (e.g., cellular) communication technology standards improve over the previous generation's data throughput. It is expected that the so-called fifth generation (5G) wireless communication systems and networks will dramatically (e.g., about twice as much) increase the data throughput of the previous generation.
Existing wireless communication systems and networks (including current generations) employ duplexing. Namely, either frequency division duplex (FDD) or time division duplex (TDD) has been used for separate transmission and reception in different frequencies or at different times respectively. In FDD and TDD, transmitted signal does not interfere with received signal due to a separate use of frequency and time resources respectively. Therefore, twice the amount of frequency and/or time are used in current duplexing systems compared to in-band full-duplex (IBFD) systems. It seems possible to double data throughputs by simultaneous transmission and reception in the same frequency band at the same time.
In addition to in-band full-duplex (IBFD) operation, mobile-communications devices may also utilize multiple reception antennas and/or multiple transmission antennas. With multiple antennas in the same mobile-communications device, the device (i.e., node) transmits and/or receives simultaneously in the same, similar, or common frequency band. Because of this, one the biggest practical impediments of the use of multiple antennas in the same device is the presence of self-interference. That is, the interference caused by transmissions from or signals reception by the other antenna(s).
Many conventional approaches utilize two separate antennas that are spaced apart. The antenna pairs have a high isolation level (e.g., ˜40 dB) with a relatively large separation and each antenna is dedicated to either signal transmission (TX) or reception (RX). While this dual-antenna approach eliminates a lossy and large circulator, it introduces new problems. The primary problems of this dual-antenna approach are space and complexity. Two separate and isolated antennas require more space because there are twice as many antennas, and those antennas must be physically spaced from each other sufficiently enough to reduce interference therebetween.
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